In many applications, highly purified starches have to be used. Protein-, fibre- and/or lipid-containing materials, such as cereals, flours and processing side-products can not be used because of the contaminating effects or deteriorating functionality of products made thereof, as a result of the non-starch components. Examples can be found in industrial non-food applications like paper, textile, adhesive, water purification, mining and oil drilling, and various more.
In paper and cardboard industry, traditionally, starches are used as a fibre-reinforcing component on a large scale and in large volumes. In particular, these starches are introduced into the paper fibre mass by means of a so-called size press. Similar applications are found in related fields such as that of the manufacture of textiles, non-wovens, tissues, and fibreboard.
U.S. Pat. No. 3,859,108 describes the use of flour in sizing paper and cardboard. Up to then, it was the general belief that proteins, such as the gluten present in flour, had a contaminating effect and caused lump formation and depositions in the system. Hence, the gluten in flour was first washed from the flour. On the contrary, U.S. Pat. No. 3,859,108 teaches that the proteins rather have a positive effect and can even take over the function of a part of the conventionally required starch. The economically unprofitable drying and purifying steps can thus be dispensed with. Thereto, the protein fraction of the flour should be maintained in substantially non-degraded form, i.e. retaining the physical properties of soluble proteins in solution. The starch is degraded enzymatically, e.g. using α-amylase, or chemically, using H2O2, so as to reduce the viscosity of the flour paste, after which the flour is cooked conventionally.
WO-A-97/10385 also relates to a method for manufacturing paper or cardboard incorporating treated flour. The flour, chemically unmodified, is subjected to a treatment whereby starch and protein are solubilized, after which the treated components of the flour are introduced into the paper-fibre matrix in a joint step. The flour treatment should not only include the aforementioned one-step treatment as known for native starch, but also a second treatment of a deamidation reaction and/or a partial proteolysis (e.g. using neutrase) to render the gluten more water-soluble. According to the examples, it would require an acid ammonium persulfate (APS) treatment at boiling temperature, or an APS and protease treatment, or an α-amylase and protease treatment. The flour may be one of beans, peas and grains, for example wheat corn and rice grains. The preferred and exemplified embodiment encompasses chemically unmodified wheat flour.
WO-A-97/38164 attempts to improve the drainage of recycled paper pulp by adding a starch hydrolysing enzyme, preferably an amylase, prior to the separation of the water from the pulp. However, drainage of pulp has little to do with the process of adding starch to the paper-fiber matrix, and the problems that arise in that step if a source of starch high in protein content is applied.
However, it is the inventors' findings and experience that the previously described methods make use of protein-starch mixtures and that the aforementioned methods still lead to protein, NSP and-/or fibre sludge and scum build-up in (paper or card-board) production equipment over time, which has precluded the economic use of flour-based instead of starch-based sizes up to present. Evidence thereof is presented in the accompanying examples.
US-A-2004/0261659 addresses the need to improve the strength of paper provided in WO-A-97/10385. It teaches to treat a starch and protein containing mixture, such as flour, using alkali oxidation. Thus obtained are improved compositions for coating paper stock. It is silent on the process of incorporating flour in the paper-fibre matrix, and on the drawback of protein accumulation in such a process.
Similar problems related with the forming of deposits and protein lumping arise in other industrial non-food applications: Starches are used in (highly) purified form in various non-food applications because the presence of protein or NSP in products are deteriorating functionality in applications and products. Some of these non-paper applications are described in more detail below.
Many publications refer to the use of (modified) starches in aqueous fluids used for drilling of oil, gas and geothermal wells. See for example U.S. Pat. Nos. 4,652,384 and 4,650,593, in the field of well-drilling fluids. The starches are used to improve various qualities of such fluids, most specifically to control filtrate or fluid losses, while having a minimum impact on viscosity. Other application areas of starches are well-fracturing fluids. It is often reported that starch polymer or cellulosic or biopolymer that has a significant contribution to the viscosity build of a drilling fluid, is undesired. There is a special role for proteins therein. U.S. Pat. No. 4,619,772 teaches that a high protein content improves viscosity and filtration control characteristics in high temperature and pressure conditions, e.g. in oil well applications. However, the product is difficult to disperse at RT because of lumping.